The threat of speed from the A backs and the balance of the formation cause a lot of problems for the defense. That doesn't mean from time to time you couldn't sneak in a larger A back in certain situations to power block and catch the defense napping. Dwyer could be the best of both worlds. Whether CPJ would actually do this remains to be seen. I suspect he has all kinds of subtle variations and tweaks he can pull out if he wants.
But in general, I have to agree with Knox. A backs cut block and crack back a fair bit, which doesn't take the biggest guy to do. Further, they present the same conundrum the WRs do: they come out looking like they are going to block, then blow by you on a play action route. Suddenly you are trying to recover against a Wright, Peeples, or R. Jones character, all of whom are 4.4 type guys.
So I would guess we'll just see the small speedy slots with the rare guest appearance as situations dictate. And I would say we are probably more likely to see any so-called "guest appearences" after a season or two, when the offense is fully installed and humming.